Here is a bizarre contradiction: the year’s biggest West End theatrical opening so far actually has disconcertingly little to do with theatre. Peter Morgan has solid form as a writer of recent-historical dramas for both stage and screen (The Deal, Frost/Nixon); it is Stephen Daldry’s first return to directing on a London stage since the 2005 stage premiere of Billy Elliot The Musical; Helen Mirren is now seen all-too-rarely on the boards, and here is supported by a phalanx of stage names including Richard McCabe, Haydn Gwynne and Paul Ritter. But that’s the very point: we are not going to this production (as we inevitably will, in droves) to see a depiction of the Queen’s weekly meetings with the various prime ministers of her reign, an assortment of character sketches and discreet musings on the tension between high office and the individual holding it. No, we will go to see Mirren, directed by Daldry, playing the Queen, and so forth.

To be sure, Mirren is excellent, whizzing through a series of onstage quick-changes in which the years (up to 60 of them) are donned and doffed as easily as what Her Majesty at one point calls her “eccentric costume”. She (and Morgan’s script) catches well what we think we know of the dry royal humour, often gently withering but never malicious.

Of her prime ministers, Richard McCabe stands out as Harold Wilson, beginning as a rumbustious class warrior (implausible as it is for Buckingham Palace to put a former Oxford don in such awe) but mellowing to a relationship of mutual banter and even, at the end, personal confidence. Edward Fox is a natural Harold Macmillan, but since Macmillan is not in this play (nor are Alec Douglas-Home, Edward Heath or, surprisingly, Tony Blair) he gives his best shot as Winston Churchill, replacing the suddenly indisposed Robert Hardy. Fox works hard to catch the great man, but in any conflict with the actor’s natural manner Churchill tends to come off second. John Major also excels – what unlikely words! – in Paul Ritter’s performance. More onstage time than any prime minister is occupied by Young Elizabeth (on press night, an assured Nell Williams), in dialogue with her older self as personifying the person and the monarch respectively.

I could, in my too-frequent cavilling mode, cite a raft of verbal anachronisms and protocol howlers that you could drive the Gold State Coach through, but – much as the production would like to flatter itself to the contrary – accuracy is not what matters. What matters is the event. They should play the national anthem at curtain-call both to compel and legitimise a standing ovation.